So we built a paltry 4,400 in the past, let's shoot for 44,000 units next year. At the already-negotiated 18% BMR, that's 7,920 price-controlled units, a massive increase in affordable housing capacity.

This line of reasoning is too simplistic. You have to look at the economic effects of the other 36,080 new high income earners, who will create new service industry jobs and thus place more pressure on afffordable housing. The BMR percentage may need to be substantially higher than that to relieve the restaurant crisis.

And that is exactly the volume vs. percentage schism I'm talking about. You're taking an increase in volume as something the other side wants, a concession that might be made in exchange for something you want.

Market rate housing does not spontaneously generate high income workers. Industry recruits them, regardless of housing construction. Those tens of thousands of workers are coming either way; the variable that can be controlled here is whether they gentrify existing buildings or divert to new ones. They're going to create more affordable-housing need by displacing people in existing units than they would in infill.

And if the BMR ratio goes up so high that projects don't pencil out anymore, then what?

Do you agree that there is a limit at which developers will just refuse to build more housing, affordable or not?